Light emitting diodes (LEDs) emitting white light are next-generation light emitting device candidates which can replace fluorescent lights, as the most representative conventional lights.
Light emitting diodes have low power consumption as compared to conventional light sources and are environmentally friendly because they do not contain mercury, unlike fluorescent lights. In addition, light emitting diodes have advantages of long lifespan and high response speed as compared to conventional light sources.
There are three methods for producing white light emitting diodes. These methods include implementation of white light by combination of red, green and blue LEDs, implementation of white light by applying a yellow phosphor to blue LEDs and implementation of white light by combination of red, green and blue LEDs with a UV LED.
Of these, the implementation of white light by applying the yellow phosphor to blue LEDs is the most representative method for obtaining white light using light emitting diodes.
White light emitted by this method has high brightness, but readily causes scintillation resulting from color separation due to great wavelength gap between blue and yellow, thus making mass-production of white LEDs having the same color coordinates difficult.
Furthermore, it is not easy to control color temperature and color rendering index (CRI) which are essential factors in light sources for lights.
Under this situation, in an attempt to solve these disadvantages, emission spectrums are widened by adding phosphors emitting red light, but there is a need for further research on development of materials for phosphors emitting red light and improvement of efficiency.